An Additivity Scheme for Aromaticity: The Heteroatom Case

The nucleus-independent chemical shift (NICS)-XY-Scan is a simple and easy tool for the quantitative measurement of the aromaticity of polycyclic aromatic hydrocarbons and identification of the existence of local and global ring currents. We recently introduced an additivity scheme that uses the NICS-XY-Scans of smaller building blocks to predict the aromatic profiles of larger polycyclic aromatic hydrocarbon systems. We now report on an expansion of the methodology to include systems of varying aromatic natures containing the heteroatoms B, N, O, and S. The additivity approach allows for rapid and resource-efficient generation of NICS-XY-Scans of large, complex systems. Moreover, it reveals that the magnetic criterion of aromaticity behaves in an additive manner, and that the ring currents of multi-ring systems appear to be mostly localized within subunits of up to three rings.     

桥环三元环苯的结构和芳香性研究

用Gaussian 03程序,采用密度泛函理论方法,对桥环三元环苯的结构和芳香性进行研究,优化得到了其稳定平衡构型,讨论了结构,通过核独立化学位移（NICS）和分子轨道（MO）分析,确定了桥环三元环苯的芳香性与键的定域之间是没有联系的,分子中的各个环的环电流大小是由取代基所决定的．     

Calculation of Fundamental Thermochemical Parameters of Phosphoranes by the Additivity Scheme

Using the additivity scheme, experimental enthalpies of vaporization and formation of phosphoranes were analyzed, group contributions to the enthalpies of vaporization and formation were determined, and thermochemical parameters of five-coordinate phosphorus derivatives were calculated.     

An Extended Group Additivity Method for Polycyclic Thermochemistry Estimation

Automatic kinetic mechanism generation, virtual high‐throughput screening, and automatic transition state search are currently trending applications requiring exploration of a large molecule space. Large‐scale search requires fast and accurate estimation of molecules' properties of interest, such as thermochemistry. Existing approaches are not satisfactory for large polycyclic molecules: considering the number of molecules being screened, quantum chemistry (even cheap density functional theory methods) can be computationally expensive, and group additivity, though fast, is not sufficiently accurate. This paper provides a fast and moderately accurate alternative by proposing a polycyclic thermochemistry estimation method that extends the group additivity method with two additional algorithms: similarity match and bicyclic decomposition. It significantly reduces H_f(298 K) estimation error from over 60 kcal/mol (group additivity method) to around 5 kcal/mol, C_p(298 K) error from 9 to 1 cal/mol/K, and S(298 K) error from 70 to 7 cal/mol/K. This method also works well for heteroatomic polycyclics. A web application for estimating thermochemistry by this method is made available at http://rmg.mit.edu/molecule_search .     

对取代苯Ph一X（X＝F，OH，NH_2）的价键理论研究

采用键表酉群方法对Ｃ６Ｈ５Ｆ、Ｃ６Ｈ５ＯＨ和Ｃ６Ｈ５ＮＨ２中的电子离域现象进行了计算和分析，讨论了取代苯的价键描述特性，并计算了取代基的π电子离域能．结果表明离子结构成分与离域能有直接关系，即离子成分越多，电子离域能越大．／６－３１Ｇ基组及“分子中的原子”方法将电荷密度分区积分得到各原子上的电荷集居数，并将此结果与取代苯的反应性能进行了比较。为在价键意义上分析和理解取代基对苯环电子结构及其反应性能的影响，本文对３个典型的取代苯Ｐｈ－Ｘ（Ｘ＝Ｆ，ＯＨ，ＮＨ２）进行了初步的价键计算和讨论．１计算方法及构型在键表酉群方法中［５］，体系的一个共振结构可用一个价键结构函数即键表ψ（ｋ）来描述，相应的体系总波函数Ψ可表示为Ｍ个正则键表的线性组合：式（１）便构成了键表相互作用（ＢＴＩ）计算方法［６］的基础．键表对体系的结构贡献定义为：原子轨道ｑ上的电荷集居数定义为：式中ｍｑ（ｋ）可取０、１或２，分别对应于键表ψ（ｋ）中原子轨道ｑ出现０、１或２次．为简比计算，我们将取代苯的σ骨架用ＨＦ分子轨道固定［７］，这样仅需考虑π电子及轨道．原子轨道积分及ＨＦ－ＳＣＦ计算采用Ｇａｕｓｓｉａｎ８０程序．联系人及第一作者：莫亦荣，男，２９     

Phendione in the Synthesis of Annelated Derivatives of 4,7-Phenanthroline

By condensation of 5-phenyl-1,3-cyclohexanedione with 6-quinolylamine and aldehydes of aromatic, heterocyclic, and cyclohexene series new 12-aryl(heteryl, cyclohexenyl)-9-phenyl-8,9,10,12-tetrahydro-7H-benzo[b][4,7]phenanthrolin-11-ones were prepared. The presence of diastereomers in the target reaction products was determined by ¹H NMR spectroscopy.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 742–748.Original Russian Text Copyright © 2005 by Gusak, Tereshko, Kozlov.     

确定大分子体系电荷分布的新方法

近年来，应用密度泛函理论探求电负性和硬度与体系中电荷分布之间的关系，成为令人关注的课题[1~5]．Mortier[1,2]的电负性均衡方法（EEM）没有考虑化学键电荷．Ghosh[4]的半经验电负性均衡方法考虑了化学键电荷，但键电荷取值假设太简单．本文同时考虑了分子中的原子电荷和键电荷的作用，给出了分子中原子和化学键有效电负性的精密公式，这些公式为发展一个系统的精密电负性均衡方法及应用奠定了基础．1理论方法以密度泛函理论[6]为基础，将分子的单电子密度ρmol（r）按式（1）分割：式中ρα（r）是分子中α原子区域的单电子密度，ρα…     

单取代苯分子中的电荷分布与定位效应

本文报道了一种简便计算一元取代苯分子中碳原子电荷分布的新方法,找出了判断定位效应的经验规则。     

Additivity of resonance energy in benzenoid hydrocarbons

A simple method is described for the calculation of resonance energies (RE ) of linear acenes based on their number of Kekulé structures. The values obtained for the first five linear acenes are used to graph–theoretically calculate RES of a wide variety of benzenoid hydrocarbons. Excellent linear relationships are found between RES and each of A-II, graph-theoretical (GT ), Hess–Schaad (HS ), and Dewar resonance energies (SCF ). These relations apply to 42 hydrocarbons and lead to the following equations: A-II = 0.084RE + 0.080 (0.9999); GT = 0.072RE + 0. 135 (0.9832); HS = 0. 106RE + 0. 169 (0.9889); and SCF = 0.316RE + 0. 166 (0.9899). Correlation coefficients are shown in parentheses. A linear relation also exists between RES and the square roots of the wavelengths of the UV spectra of hydrocarbons of the linear acenes and phene series. Least-squares analysis of the data leads to the following equation: RE = 0.412(λ)^½ ?15.479, with a correlation coefficient equal to 0.9903, in which λ is the wavelength of the β band of the UV spectra of these hydrocarbons. The method predicts no resonance energies for both open chain polyenes and the radialenes.     

Phenalenannulations: Three-Point Double Annulation Reactions that Convert Benzenes into Pyrenes

3-Point annulations, or phenalenannulations, transform a benzene ring directly into a substituted pyrene by “wrapping” two new cycles around the perimeter of the central ring at three consecutive carbon atoms. This efficient, modular, and general method for π-extension opens access to non-symmetric pyrenes and their expanded analogues. Potentially, this approach can convert any aromatic ring bearing a -CH₂Br or a -CHO group into a pyrene moiety. Depending upon the workup choices, the process can be directed towards either tin- or iodo-substituted product formation, giving complementary choices for further various cross-coupling reactions. The two-directional bis-double annulation adds two new polyaromatic extensions with a total of six new aromatic rings at a central core.     

空气中苯系物测定有关问题的探讨

对HJ 584–2010《环境空气苯系物的测定活性炭吸附/二硫化碳解吸–气相色谱法》和HJ 583–2010《环境空气苯系物的测定固体吸附/热脱附–气相色谱法》进行解析,结合监测工作实际情况,从采样、分析各个关键环节总结归纳了方法要点,提出了实际应用中的注意事项。为环保监测系统进行空气中苯系物测定方法的选择及正确应用提供借鉴。     

Additivity of noise propagation in a protein cascade

Stochastic fluctuations in a protein synthetic cascade are investigated using standard Omega-expansion technique. For the steady-state sensitivity, we show the conditions that result in the ultrasensitive "all-or-none" behavior, and for the noise propagation, we show clearly that (i) for any one given protein species in this cascade, the contributions of fluctuations in upstream proteins to its noise should be additive; and (ii) the output noise levels can vary as a function of the input concentrations and cascade length. Our results provide a possible theoretical explanation for the previous experimental studies.